Technique for correcting the crystallographic orientation angle of crystals by double face lapping of overlapping layers

ABSTRACT

A technique for accurately correcting the crystallographic orientation angle of crystal plates comprises the steps of arranging a plurality of plates in two overlapping layers, double face lapping the overlapping layers to remove a wedge or section of material from one major surface of each plate to thereby change the orientation of the plate, and making the other major surface of each plate parallel with the first major surface. The amount of angle correction is determined by such factors as the amount of overlap of the two layers and the lapping time.

United States Patent 11 1 Miller TECHNIQUE FOR CORRECTING THE CRYSTALLOGRAPHIC ORIENTATION ANGLE OF CRYSTALS BY DOUBLE FACE LAPPING OF OVERLAPPING LAYERS Inventor: Anton Johann Miller, Allentown,

Bell Telephone Laboratories, Incorporated, Murray Hill, NJ.

Filed: Dec. 22, 1972 Appl. No.: 317,717

Assignee:

US. Cl. 51/283, 51/327 Int. Cl B24b 1/00 Field of Search 51/281 R, 281 SF, 283,

References Cited UNITED STATES PATENTS 3,123,953 3/1964 Merkl ..51/2s3 Apr. 23, 1974 2,378,243 6/1945 Penberthy 5l/283 X 3,603,039 9/l97l Stahr 5l/283 3,562,965 2/1971 Lange 51/283 Primary ExaminerAl Lawrence Smith Assistant Examiner-Marc R. Davidson Attorney, Agent, or Firm-A. D. Hooper [5 7] ABSTRACT A technique for accurately correcting the crystallographic orientation angle of crystal plates comprises the steps of arranging a plurality of plates in two overlapping layers, double face lapping the overlapping layers to remove a wedge or section of material from one major surface of each plate to thereby change the orientation of the plate, and making the other major surface of each plate parallel with the first majorsurface. The amount of angle correction is determined by such factors as the amount of overlap of thetwo layers and the lapping time.

I 8 Claims, 14 Drawing Figures PATENTED PR 23 :91;

SHEET 5 IF 6 FIG. 7

w 9 T l l/ 0U Q\ \P 7 o 9% b V s v b 6 Q Q I b/ Q Q/ S 4 vw/ QM. 3 2 II I O m w w w m m o AMOUNT OF ANGLE CORRECTION A6 IN MINUTES OF ARC FIG. 8A F/G.8B FIG. 8C F/GT8D +X TOP PLATE BOTH PLATES TOP PLATE BOTI-I PLATES 9 DECREASES 9 DECREASES 9 INCREASES 9 INCREASES BOTTOM PLATE 9 DECREASES BOT TOM PLATE 9 INCREASES 1 TECHNIQUEFOR CORRECTING THE CRYSTALLOGRAPHIC ORIENTATION ANGLE OF CRYSTALS BY DOUBLE FACE LAPPING OF OVERLAPPING LAYERS BACKGROUND OF THE INVENTION plications call for plates having crystallographic orientation angles with seconds of are or less of a specified value. However, cutting accuracy is at best not nearly this precise. Thus, after the cutting operation crystal plates for precision applications must have the orientation angles thereof corrected or many of the plates must subsequently be-rejected.

Present apparatus and methods for correcting orientation angles of crystal plates are not adequate to provide the tolerances previous mentioned. Such apparatus usually comprises a diamond grinding wheel and a chuck upon which the plates to be corrected are mounted one at a time. The relative positions of the wheel and the chuck holding the plate being corrected are controlled by micrometers. This apparatus has acapability of correcting the orientationangle of a crystal plate to an accuracy of approximately :2 minutes of are which is not sufficient for many applications. Another disadvantage of this apparatus is that only one plate can be corrected at-a time. Still another disadvantage of this apparatus is that the diamond grinding operation leaves an undesired surface condition on the plate which must subsequently be removed.

In view of the foregoing disadvantages of the present .for high precision'applications. For example, many apapparatus and methods, crystal plates for precision applications are normally carefully selected from production plates. This selection process results in very low yields of usable plates for specific applicationsand accordingly high costs for the crystalplates. Thusa need remains for a method of correcting the orientation angle of crystal plates to provide economical yieldsof such plates for precision applications.

Accordingly, it is an object of this invention to improve the methods for correcting the crystallographic orientation angle of crystal plates to allow simultaneous correction of a plurality of crystal plates.

Another objectis to improve the methods of correcting the orientation angle of crystal plates to provide more precise corrections.

SUMMARY OF THE INVENTION The foregoing objects and others are achieved in ac: cordance with the invention by arranging a plurality of crystalplates to be corrected in two overlapping layers. The overlapping layers are placed in a planetary lapping machine where they are double face lapped to remove a wedge orsection of material from a major surface of each plate. to thereby correct the crystallographic orientation. The amount of correction is determined by the amount of overlap andthe lapping time.

tation angle; and

The plates are then subjected to further double face lapping to make the other major face of the crystal I plate parallel with the corrected face.

BRIEF DESCRIPTION OF THE DRAWING The invention will be more fully comprehended from thefollowing detailed description and accompanying drawing in which:

FIG. 1 is a perspective view of a crystal plate indicating the desiredorientation angle correctionthereof;

FIG. 2 is an exploded perspective view of a plurality of crystal plates arranged for correction of the orientation. angle;

FIGS. 3A and 3B are cross-sectional views of an arrangement of crystal plates similar to FIG. Zmounted between lapping plates for the first step of the angle correction process of this invention;

FIGS. 4A and 4B are schematic sectional representations of the second step of the angle correction process in a first embodiment of the invezntion;

FIG.5 is a schematic sectional representation of the third process step in a first embodiment of the invention;

FIG. 6 is a schematic sectional representation of the second step in a second embodiment of the invention;

FIG. 7 is a characteristic plot ofthe relationship of lapping time and degree of overlap to the amount of angle-correction;

FIGS. 8A through D are schematic representations of the various ways of arrangingthe crystalplates for obraining differentdirections ofcorrectionfor the orien- FIG. 9 is a plan view of one possible layout of crystal plates on the carrier of a planetary lapping machine.

The relative dimensions shown in the drawing are merely for. purposes of illustration and are. greatly exaggerated in many instances.

DETAILED DESCRIPTION thedesired tolerances by existing manufacturing techniquesAccordingly, the orientation angle of the crystal plate must be changed by an amount A0 if the plate is to operate satisfactorily in precision applications. This is accomplished by'removing wedges or sections 12 and I4-of material from the major surfaces orfaces 16 and 17, respectively, of plate 1050 that to a very close approximation A0 S/R where A0 is the desired amount of angle correction, :R is the Z2 dimensionof the plate, i.e., isthe length of surface 16, and S is the maximum thickness of the wedge 12 of material removed. The thickness S required to provide the final orientation change of A0 can be considered as one angle unit of material. It should be kept in mind that thickness S applies "only to a generalized wedge 12 of material, the removal of which will change the orientation angle of plate 10 by a net amount A0. The actual thickness of a section of material removed from plate 10 in any given step of the correction procedure may I and 17 are again made parallel by the removal of wedge 14 from surface 17.

FIG. 2 is an exploded perspective view of an arrangement of crystal plates for removing the appropriate wedges of material for orientation angle correction by double face lapping in accordance with this invention. Two layers 20 and 22 of crystal plates 10 are arranged in an overlapping configuration and a free floating condition within an aperature 24 of a holder or carrier 26 of a lapping machine which is to be utilized to remove the appropriate sections of material. The amount of overlap of layer 20 and 22 is determined by the amount of angle correction desired as will be discussed subsequently. This overlap is controlled by spacers 28a and 28b. Spacer 28a spaces or positions layer 22 with respect to a first side or edge 25 of aperture 24 and spacer 28b spaces layer 20 with respect to the opposite side 27 of aperture 24. Thus the degree of overlap can be determined by the width 29a and 29b of the respective spacers 28a and 28b.

FIG. 3A is a schematic cross-sectional representation I of the plate arrangement of FIG. 2 after installation of carrier 26 in a double face lapping machine, such as a planetary double face lapping machine, to remove the appropriate wedges of material. Appropriate lapping machines are well known in the art. The overlapping layers 20 and 22 of crystal plates 10 are arranged between upper and lower lapping plates 30 and 32, respectively, and subjected to lapping motion. The force balance within the double face lapping machine, i.e., the force balance between plates 10 and lapping plates 30 and 32, is such that the same amount and configuration of material is removed from the exposed major surfaces or faces 33 of plates 10 in each of the layers. The

force balance also dictates that more material is removed from the overlapping portion of plates 10 than from the nonoverlapping portions. Accordingly, generally wedge-shaped portions on sections 34 of material will be removed from the exposed faces 33 of each plate 10 as shown by the dashed lines 34a.

The dimensions of the removed section 34 as compared with the dimensions of the corrective wedge 12 shown in FIG. 1 depends upon the subsequently anticipated processing steps. For example, if the desired angle correction is A the maximum thickness 35 of section 34 removed in the initial lapping step of FIG. 3A-B may need to be equal to S or to twice S depending upon the subsequently anticipated steps, i.e., section 34 may comprise either one or two angle units, as will now be discussed with reference to two embodimentsof the technique.

In the first embodiment, sections 34 of material re moved by the initial double face lapping step of FIGS. 3A and 38 comprise one angle unit, i.e., the maximum thickness 35 of sections 34 equals thickness S discussed with respect to FIG. 1. After the removal of sections 34 the layers 20 and 22 of plates are flipped over as shown in FIG. 4A in section so that the previously exposed and lapped surfaces 33 of plates 10 now overlap and the previously overlapping surfaces 36 arenow exposed to lapping plates 30 and 32. Plates 10 have also been rotated 180 so that the previously overlapping ends no longer overlap while the previously nonoverlapping ends now overlap. Plates 10 are subjected to a second double face lapping until section 37 of material indicated by dashed lines 37a substantially identical to sections 34 have been removed from newly exposed surfaces 36. Sections 37 and 34 are rotated from each other as shown by dashed lines 37a and phantom sections 34 respectively, in FIG. 4A. When this lapping step has been completed the major surfaces 33 and 36 of crystal plates 10 are again parallel as indicated in FIG. 4B and the orientation of the plate has been changed by the desired amount A0.

To remove any surface irregularities remaining from the lapping during the overlaying configuration it is normally desirable to rearrange plates 10 into a single layer in a carrier 41, as shown in section in FIG. 5, and perform an additional double face lapping thereof. During the lapping while in a single layer configuration very small equal sections 38 of material are removed from both major surfaces 33 and 36 of plate 10-as indicated by dashed lines 38a so that the previously corrected orientation angle and parallel condition of sur-- faces 33 and 36 are not disturbed.

In a second embodiment of the invention, the sections 34 of material removed by the initial double face lapping step of FIGS. '3AB comprise two angle units, i.e., the maximum thickness 35 of sections 34 is twice the thickness S. Such a section of material would produce a change in the orientation angle of twice the de sired amount A0 if a portion of this change were not recovered in subsequent steps by a removal of another section of material having an opposite effect on angle change. Accordingly, after removal of a double amount or double angle unit section 34 by the initial double face lapping shown in FIGS. 3A-B, plates 10 are rearranged in a single layer within a carrier 40 between lapping plates 30 and 32 as shown in section in FIG. 6, which shows section 34 including two subsections 34c and 34a' each of which comprises one angle unit. The plates 10 are then subjected to a double face lapping which because of the force-balance removes substantially identical sections 42 of material as indicated by dashed lines 42a having thicknesses 44 equal to S from faces 33 and 36 thereof. Sections 42 are oriented in the opposite direction of section 34 shown in phantom. Thus the net effect of the removal of sections 42 is the recovery of one angle unit of rotation and the making of surfaces 33 and 36 parallel. Accordingly, plate 10 ends up with anet angle change of A0 as desired and smooth parallel surfaces 33 and 36. After the removal of sections 42 there is no need for further lapping because sections 42 were removed by lapping while plates 10 were arranged in a single layer.

The first described embodiment of the invention offers the advantage that a minimum amount of material is removed from plates 10 to effect the desired angle change. The second described embodiment results in the loss of more material from plates 10 but has the advantage of eliminating the requirement for rearrangement and a second double face lapping of plates 10 while arranged in overlapping layers. Either embodiment provides precision correction of the orientation angle of crystal plates.

The amount of angle correction, i.e., the number of angle units of rotation provided by section 34, depends upon variables such as the amount of overlap of layers 20 and 22, the lapping time, the lapping machine speed, the weight of the upper lapping plate 30, the

- characteristics of the abrasive and slurry utilized, the

number of plates being corrected in a specific batch, et

cetera. The variables of lapping time and degree of overlap advantageously can be used to control the angle correction. FIG. 7 is a characteristic plot of lapping time versus amount of angle correction for various overlapping conditions utilizing the second embodiment of the invention, i.e., where the maximum thickness 35 of section 34 initially removed is twice the thickness S required to produce the desired orientation change A6. The values shown are merely illustrative and in no way restrict the scope of the invention. The lapping time is probably the most advantageous variable for controlling the amount of angle correction.

The actual direction of angle correction depends upon the orientation of crystal plates 10 within overlapping layers and 22 with respect to each other. FIGS. 8A through D schematically illustrate four possible arrangements of crystal plates 10 with reference to their crystallographic axes x and ZZ' and the resulting direction of angle correction with respect to the Z2 axis. Accordingly, it should be apparent that any amount and direction of angle correction can be obtained in accordance with this invention. Different directions of correction can be provided for the different crystal plates 10 within a specified group or batch being corrected by merely arranging the orientations of various overlapping pairs of plates 10 as shown. -As previously indicated the angle correction tech nique of the invention can be utilized for simultaneously correcting the orientation angles of many crystal plates 10. This is a significant advantage over existing methods which require individual correction. Advantageously a four-motion planetary lapping machine such as those well known in the art can be utilized to implement the correction technique of this invention. Four-motion planetary lapping machines subject the crystal plates and carriers to less stress than do the twomotion machines. Further the crystal plates can be more closely positioned in the four-motion machines.

FIG. 9 illustrates one possible layout of the crystal plates 10 on one carrier 56 of a four-motion planetary lapping machine utilizing 50 percentoverlap. Three pairs 50, 51, and 52 of overlapping layers 50a and 50b, 51a and 51b, and 52a and 52b, respectively, of plates 10 are shown. The number of plates 10 which can be mounted on a single carrier 56 depends of course upon such factors as the degree of overlap, the size of the carrier 56, et cete ra. The number of carriers available depends upon the particular machine being utilized. For example, in excess of one hundred crystal plates 10 each of which is 1.4 inches long and 0.5 inches wide can be corrected simultaneously on a large planetary lapping machine utilizing 50 percent overlap. The only limitation on simultaneous correction of a plurality of plates is that the plates have approximately uniform initial thicknesses.

Crystal plates can be corrected much more accurately by the foregoing double face lapping technique than by any existingtechniques. The lapping time can be used to very accurately control the dimensions of the wedge or section 34 of material removed from the plate and thereby control the angle correction.

While the invention has been described with reference to specific embodiments thereof, it is to be understood that various modifications thereto might be made by those skilled in the art without departing from its spirit and scope.

I claim:

1. A method of changing the crystallographic orientation angle of crystal plates comprising the steps of:

arranging said plates in firse and second layers so that a first surface of one of said plates in said first layer overlaps a portion of a first surface of a corresponding plate in said second layer; double face lapping said two layers of plates to remove a first wedge of material from second surfaces thereof opposite said first overlapping surfaces to thereby change said orientation angle; and

making said first surfaces of said plates parallel to said second surfaces.

2. The method of claim 1 wherein said making step includes the steps of:

flipping said two layers over so that said second surfaces of said corresponding plates overlap; and double face lapping said two layers to remove a second wedge of material from said first surfaces of said plates to make said first surfaces parallel to said second surfaces, saidsecond wedge being rotated substantially 1S0 degrees 'with"respect to said first wedge.

3. The method of claim 2 further including the step of rearranging said plates into a single layer; andv double face lapping said single layer of plates.

4. The method of claim 2 wherein said first-wedge of material has a maximum thickness defined by S RAH where S is said maximum thickness, R is the length of said wedge along said second surface and A0 is the preselected amount of change in said orientation angle.

5. The method of claim 1 wherein said making step includes the steps of: l

rearranging said plates into a single layer; and double facelapping said plates to remove second and third wedges of material from said first and second surfaces, respectively, said second and third wedges being rotated su b s tantialTy l wdegre es with respect to said first wedge. 6. The method of claim 5 wherein said first wedge has a maximum thickness defined by S 2RAO and said second andthird wedges are substantially identical and have maximum thicknesses defined by S RAO where S is the maximum thickness of said wedge indicated by the subscript, R is the length of said plate, and A0 is the preselected amount of change in said orientation angle.

7. The method in accordance with claim 1 wherein said arranging step includes the steps of:

placing said first and second layers in an overlapping configuration within an aperture of a carrier on a planetary lapping machine; and

installing first and second spacers to space said first.

responding plate in said second layer. 

1. A method of changing the crystallographic orientation angle of crystal plates comprising the steps of: arranging said plates in firse and second layers so that a first surface of one of said plates in said first layer overlaps a portion of a first surface of a corresponding plate in said second layer; double face lapping said two layers of plates to remove a first wedge of material from second surfaces thereof opposite said first overlapping surfaces to thereby change said orientation angle; and making said first surfaces of said plates parallel to said second surfaces.
 2. The method of claim 1 wherein said making step includes the steps of: flipping said two layers over so that said second surfaces of said corresponding plates overlap; and double face lapping said two layers to remove a second wedge of material from said first surfaces of said plates to make said first surfaces parallel to said second surfaces, said second wedge being rotated substantially 180 degrees with respect to said first wedge.
 3. The method of claim 2 further including the step of rearranging said plates into a single layer; and double face lapping said single layer of plates.
 4. The method of claim 2 wherein said first wedge of material has a maximum thickness defined by S R Delta theta where S is said maximum thickness, R is the length of said wedge along said second surface and Delta theta is the preselected amount of change in said orientation angle.
 5. The method of claim 1 wherein said making step includes the steps of: rearranging said plates into a single layer; and double face lapping said plates to remove second and third wedges of material from said first And second surfaces, respectively, said second and third wedges being rotated substantially 180 degrees with respect to said first wedge.
 6. The method of claim 5 wherein said first wedge has a maximum thickness defined by S1 2R Delta theta and said second and third wedges are substantially identical and have maximum thicknesses defined by S23 R Delta theta where S is the maximum thickness of said wedge indicated by the subscript, R is the length of said plate, and Delta theta is the preselected amount of change in said orientation angle.
 7. The method in accordance with claim 1 wherein said arranging step includes the steps of: placing said first and second layers in an overlapping configuration within an aperture of a carrier on a planetary lapping machine; and installing first and second spacers to space said first and second layers, respectively, from first and second sides of said aperture thereby to control the degree of overlapping of said first and second layers.
 8. The method in accordance with claim 1 wherein said first surface of said plate in said first layer overlaps approximately one-half of said first surface of said corresponding plate in said second layer. 